This invention relates to controllers for electrically-actuated braking systems such as those used to apply the brakes on towed vehicles, i.e., trailers, in response to commands from the towing vehicle. More particularly, the invention relates to electronic controllers for braking systems of the general type just noted which operate in response to inertial sensors and/or manually-actuated switches, or the like, to energize electric brake-actuation components of such systems in a particular controlled manner.
Substantial effort and progress continues toward the goal of providing more stable and more responsive electronic brake system controllers which apply drive excitation to the electromagnetic brake shoe actuators located at the trailer wheels. A number of difficulties have been encountered in providing electronic controllers for such towed vehicle electromagnetic brake shoe actuators. For example, continuous braking excitation is likely to promote trailer brake lockup, and that is a most undesirable event since it brings about a marked decrease in braking efficiency and loss of operator control. One technique for avoiding continuous braking excitation involves applying pulsating excitation to the electromagnetic actuators. Such pulsating excitation systems may be in the form of a constant pulse-width applied at varying frequencies or a varying pulse-width applied at a constant frequency. However, variable frequency systems usually include some actuation frequencies which unfortunately complement, or reinforce, resonant frequencies in the vehicle braking system (whether mechanical, electromechanical or electromagnetic in nature) with the result being instability, brake chatter, etc. Pulse-width-modulated (variable-pulse-width) constant-frequency systems sometimes utilize operational frequencies which have such adverse characteristics, and are likely to have other disadvantages as well.
One common incident of practically all state-of-the-art electronic brake-system controllers is the fact that they utilize, and in fact require, interconnection with the vehicle brake light circuit. However, where the brake light signal is required to activate the towed vehicle brakes, mechanical or electrical failure in the brake light circuit entirely extraneous to actual towing vehicle performance could result in the loss of all trailer braking. Furthermore, with the increasing sophistication of modern-day vehicles, the brake light circuit has grown increasingly complex, since it is now directly intercoupled with such other systems as electronic cruise controls, antiskid braking systems, etc., and as a result each such system becomes more interdependent and subject to failure or malfunction caused by the others. Additionally, trailer brake controllers are after-market devices which are installed after the tow vehicle leaves the factory. Thus, with the increasing complexity of vehicles and systems related to the brake light actuation system, it becomes increasingly more difficult, as well as more risky and potentially damaging, to physically breach the factory-installed wiring in order to interconnect the brake light actuation system with after-market devices.
Thus, it is desirable to provide electronic brake controllers for towed vehicles which are relatively easy to install without risk of damage to the electronic controller or the towing vehicle factory-installed wiring. A particularly advantageous system is disclosed in U.S. Pat. No. 5,090,937, wherein an electronic controller for actuating the brake system is independent of the towing vehicle brake light actuation system. While the system of this patent overcomes many of the problems of the prior art, and provides effective towed vehicle braking, it remains desirable to provide even more improved electronic controllers for electric brake systems.
One difficulty encountered in providing electronic controllers is accommodating different towed vehicle weights, as well as different towed vehicle electromagnetic brake system characteristics. Heavy towed vehicles require more braking current to have the same brake response as a lighter trailer. Thus, when different towed vehicles are connected to the electronic controller, the braking system will provide a different "feel" to a towing vehicle operator. Additionally, the rate at which the brakes are actuated, as set at the factory, may be different from the rate at which an operator would like them to be actuated. While known electronic controls allow a vehicle operator to select the maximum effective current applied to the electromagnetic brake actuator, they do not allow the operator to independently vary the rate at which current is applied to the electromagnetic brake actuator. Finally, different electromagnetic brake shoe actuators require different current magnitudes to initiate towed vehicle braking.
In addition, electronic controllers for electric brake systems lack adequate protection against incorrect connection of the electronic controller to the towing vehicle electrical system. In particular, the electronic controller may not be adequately grounded when it is installed. For example, where an operator mounts the controller on a vehicle dashboard, the installer may connect the controller to the dashboard for purposes of providing a ground. However, when the vehicle in which the controller is mounted is jarred, the ground connection provided by the vehicle through the dashboard may be interrupted such that the controller is temporarily disconnected from the ground. When known electronic controllers are disconnected from the ground, the voltage within the controller can increase such that it exceeds the voltage capacity of the controller integrated circuits. As a result, the integrated circuits in the controller may be destroyed.
Another difficulty encountered in electronic brake controllers is providing sufficiently rapid brake actuation without causing brake lock-up. If the effective current applied to towed vehicle brakes is increased too rapidly, the brakes may lock up. On the other hand, if the brake current is applied too gradually, the brakes may not be fully activated in a timely manner, such that brake actuation is sluggish. An additional difficulty is providing a controller which avoids the above problems, yet releases the brakes rapidly when the brake actuation signal is removed, to prevent continued actuation of the towed vehicle brakes.